Low capacitance cables

[Ron Resnick]

If you look at Tara Labs they have some really low capacitance (single digit) figures. I was looking at them for phono cables from turntable to the Io.

Which one did you select, Dan?

 

[dan31]

I ended up with a phono cable from CHacoustic. I had such a good experience with the XP20 power cable on my Io that I looked into a phono cable from them and have been very satisfied. The CHacoustic cable was made using the top of the line furutech RCA plugs and is very revealing but has an even presentation with no boosted low, mid or high frequency. Buying direct was also nice.

If I had not gone with CHacoustic I was going to demo the Taralabs Zero LX phono cable and the Cardas clear phono. Taralabs has a loaner program. I think some SME arms require a different din wiring for +/-. Best to be sure any cable you demo is wired for your planned SME arm.

 

[Speedskater]

It's the 50K input impedance that counts, not the 1K ohms output impedance.

Boy did I mess that up!!!I was rushing off to speedskating practice and put my head on backwards.

It's the output impedance that forms a low-pass filter with the total cable capacitance.

So with:
a] Output impedance = 1 kOhm
b] Cable capacitance = 100 pF/foot and 25 feet = total 2500 pF
the 20 kHz response is down 0.5 dB.
and 0.5 dB = 94%
also 10% loss = 0.9 dB

But these calculations are for a 25 foot cable not a 7 foot one.

 

[Speedskater]

Old Ampex high speed tape duplicators may have had a 5 pF/foot coax cable from the tape head. The coax was about 1/2 inch diameter and had an extremely small solid center conductor.

The lowest capaticance in common coax cables is about 12/13 pF/foot.

 

[twitch]

Boy did I mess that up!!!I was rushing off to speedskating practice and put my head on backwards.

LOL ....... or in other words a momentary lapse into 'cranial rectal inversion' !

 

[Speedskater]

LOL ....... or in other words a momentary lapse into 'cranial rectal inversion' !

Exactly!

But luckily at the rink, I didn't go fast and turn right.

 

[Uk Paul / Z:Axis Audio]

Boy did I mess that up!!!I was rushing off to speedskating practice and put my head on backwards.

It's the output impedance that forms a low-pass filter with the total cable capacitance.

So with:
a] Output impedance = 1 kOhm
b] Cable capacitance = 100 pF/foot and 25 feet = total 2500 pF
the 20 kHz response is down 0.5 dB.
and 0.5 dB = 94%
also 10% loss = 0.9 dB

But these calculations are for a 25 foot cable not a 7 foot one.

Based on your figures, I for one wouldn't be able to hear any roll off in a 3-4ft cable, hence not getting too bogged down with figures but using my sense's to determine good/not so good products.. As Dave C rightly stated, it is pretty easy to make a very low pf cable, whether it sounds better is a another thing.

 

[Speedskater]

Actually those are Bill Whitlock's calculations. I just changed 50pF & 50 foot cable to a 100pF and 25 foot cable. Same total capacitance.

While some poorly designed output stages might not like that amount of total capacitance, audio frequency roll-off won't be a problem.

 

[microstrip]

Actually those are Bill Whitlock's calculations. I just changed 50pF & 50 foot cable to a 100pF and 25 foot cable. Same total capacitance.

While some poorly designed output stages might not like that amount of total capacitance, audio frequency roll-off won't be a problem.

When we are using some one else calculations it would be nice to include a link to the original. And why should we consider that a domestic audio output is "poorly designed" because it can not drive a 25 feet cable?

Should we say the same words for anyone having a 100 kohm input impedance?

 

[Speedskater]

When we are using some one else calculations it would be nice to include a link to the original.

He writes about it in several papers, but I was looking at page #97 of:
http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

And why should we consider that a domestic audio output is "poorly designed" because it can not drive a 25 feet cable?

Because it's almost 2018, it's not 1980 anymore. But if you have legacy equipment, then don't use interconnects with high total capacitance.

Should we say the same words for anyone having a 100 kohm input impedance?

I don't see any problems here.

 

[Speedskater]

These is a very old Siegfried Linkwitz post on the subject:

Let's put a little realism into high frequency loss due to long interconnects.

I just measured 2 nF capacitance for a 5 m RCA connector cable that I use with Pluto. That is 400pF/m rather than 100pF/m or less which is typical for interconnects.

If the output impedance from the pre-amp is 1kohm (high) and the input impedance of the power amp is 10kohm, then the effective impedance is 10k//1k or 910ohm.
With the 2nF cable this gives a low-pass 3dB cutoff frequency of Fc = 1/(2piRC) = 87 kHz, which is still far above the needed frequency range. With a typical capacitance cable the cutoff would be at 350 kHz. If the passive pre-amp has 10kohm output resistance Fc would still be 70kHz.

 

[DaveC]

Yup, C is not the problem that causes highs to seem dull in some cables, although it is misunderstood or misrepresented by some to be an issue. Low-C is not an indicator of good-sounding cables either.

 

[Empirical Audio]

These is a very old Siegfried Linkwitz post on the subject:

Let's put a little realism into high frequency loss due to long interconnects.

I just measured 2 nF capacitance for a 5 m RCA connector cable that I use with Pluto. That is 400pF/m rather than 100pF/m or less which is typical for interconnects.

If the output impedance from the pre-amp is 1kohm (high) and the input impedance of the power amp is 10kohm, then the effective impedance is 10k//1k or 910ohm.
With the 2nF cable this gives a low-pass 3dB cutoff frequency of Fc = 1/(2piRC) = 87 kHz, which is still far above the needed frequency range. With a typical capacitance cable the cutoff would be at 350 kHz. If the passive pre-amp has 10kohm output resistance Fc would still be 70kHz.

3dB down at 87KHz is certainly not good enough for me. I want to see each of my components with B/W of 100kHz. Why would I want less for my cables? These roll-offs are additive. 1dB down at 30kHz for a cable may result in 3 dB down or more for the system.

It's like trying to measure a signal with frequency components of 1.5MHz with a 2MHz B/W scope. If you don't mind an inaccurate reading...

Capacitance is certainly not the ONLY attribute that makes a great interconnect cable, but an important one. More important than resistance and inductance.

Steve N.